The present invention relates to an illuminating device for the liquid crystal display device of electronic timepiece.
There has been provided an illuminating device comprising a light emitting material which effects without a voltage supply. The light emitting material is selected from radioactive materials such as promethium 147 (.sup.147 Pm), tritium (.sup.3 H) and the like. Such a radioactive material is mixed with suitable cementing material to form a light emitting paint or element. The light emitting element is coated with a transparent resin. Tritium is preferable to the light emitting element, since it has a long lifetime of which the half-life is about 12 years longer than promethium 147. However, in the light emitting element composed of tritium, difficult problems arise in the practical use thereof. More particularly, the constituents .sup.3 H atoms of tritium leak owing to the substitution thereof with H atoms in the hydrocarbonaceous resin coating, so that luminance of the element is decreased and besides there is a danger to the human body.